Insulation suggestions for expansion tank

What kind of insulation does everyone recommend wrapping around an expansion tank to prevent any freezing damage? I installed an expansion tank next to my hot water heater in the attic last year, and today I was looking through some papers, and I came across a small tag that came with the expansion tank and it had a warning that stated to replace the tank if ever subject to freezing temps (I didn't have it wrapped this last winter). I live in North Texas and winter temps can get to low 20s at night on a rare occasion with averages in low to mid 30s at night. I've closely inspected the tank and the bladder is holding air and seems to be functioning fine. I want to wrap it up for this next winter. Is the .5" thick fiberglass insulation wrap with foil backing adequate enough? The tank is suspended horizontally and supported by metal strapping so a standard tank sleeve wouldn't work too well. Any chance the tank was damaged last winter? Thanks in advance for any suggestions.

While it may be somewhat common, personally, I find it a very bad practice to have something like a WH in an area that can freeze. While it may or may not freeze, the piping to and from it certainly can and while there may be some conduction through the water, most are installed with heat traps to minimize that. By having it there, your standby losses are significantly increased (except during your summer where the WH may end up getting hot without running!). Insulation does not create heat, but slows the transfer of heat. If it gets cold enough and there's no hot water use, things will freeze. If it's an electric one, hope you don't get a prolonged power outage, either. I'd purchase the best (thickest) pipe insulation and consider maybe a roll of the foil faced bubble wrap, and wrap the tank as best I could with a bunch. Since there usually isn't much water exchange in the tank, even using hot water may not warm it enough, although the hot running by its inlet will warm it a little. An attic typically is ventilated, and any moving, cold air is your worst enemy when it comes to freezing pipes. Hopefully, someone with more local knowledge will have some more definitive suggestions.

Thanks for the quick reply. Unfortunately I don't have a choice with the design of the house, but I have all of the pipes wrapped up very well, and when the temp hits 30 degrees or below we slowly run the faucet in the northern exposed bathroom. We had a couple of pretty cold days and nights in a row this last winter and we didn't have any problems. I just got a little freaked out when I saw that label today. I thought about wrapping it with the insulation wrap and then take one of the green insulation bags made for covering back flow preventer exterior sprinkler pipes, cut the bag to fit and wrap it over the tank and zip tie it around it. Just a thought.